The present invention relates to a ground-based apparatus for the take-off, landing and taxiing of aircraft without undercarriage system or with retracted undercarriage which is additionally installed on a runway.
The empty mass of an aircraft has a major influence on its economy. A lower empty mass ensures a better economy for the same maximum take-off weight or for constant payload, as either greater payload can be transported or the air drag and therefore the fuel consumption is reduced due to the reduction in gross mass. With conventional aircraft, the undercarriage takes up a relative portion of about 6% to 10% of the empty mass depending on the aircraft type and has no function during the cruise flight. It is used on the ground for take-off, landing and taxiing. Furthermore, the undercarriage system is very cost intensive, both in manufacture and in operation. Omitting the undercarriage system would result in a reduction in the empty mass and in economic, ecological and operational advantages for the aircraft operator in regular flight operations.
To make use of these advantages, a ground-based apparatus which enables aircraft without an undercarriage to take off, land and taxi must be installed at airports.
There have been a large number of aircraft types in the history of air travel which were not fitted with an undercarriage. Technologies that have already been used and publications in connection with aircraft without an undercarriage that have not previously been implemented are highlighted below.
Basically, the solutions which have been found can be divided into two groups: solutions installed in the aircraft and solutions installed on the ground.
The first aircraft-based solutions were realized in the Second World War. The Messerschmitt Me 163 “Komet”, which was built from 1941, was a fighter-interceptor with a rocket propulsion and took off optionally on a jettisonable two-wheeled undercarriage or a ramp. Landing took place on a skid installed on the aircraft. 80% of about 370 aircraft built crashed due to landing errors.
The Arado Ar 234 “Blitz” was built from 1943 onwards. The first version was built without an undercarriage. Version A-0 of the “Blitz” was fitted with a fixed landing skid and a releasable three-wheeled take-off trolley. Take-off and landing were so impractical however that subsequent versions were fitted with an undercarriage installed on the aircraft.
The ground operations to transport these aircraft from the runway after landing, to move them onto the take-off trolley again and to retrieve the take-off trolley after every take-off were very laborious. This fact alone would make the normal operations of modern aircraft on the ground highly complicated. Furthermore, there was only limited tracking stability and no possibility of regulating the braking force when landing with a skid. The deceleration depends on the friction between the skid material and that of the airfield.
Runway-installed solutions for landing aircraft without an undercarriage were investigated by the Royal Navy from 1947 to 1955. Three prototypes of the De Havilland F21 “Sea Vampire” were modified to carry out landings with retracted undercarriage on a flexible rubber deck. Here, the runway absorbed the landing impact and the braking force resulted from the friction between the underside of the aircraft and the runway covering. After landing, the “Sea Vampire” had to be removed from the runway and placed on a ramp for take-off After numerous test runs on land, the flexible runway was installed on the aircraft carrier “HMS Warrior”. In this case, deceleration occurred in a controlled manner by means of the tail hook catching system which is in common use on aircraft carriers.
This system is not suitable for use with present-day aircraft, in particular commercial aircraft, on account of the laborious operations on the ground, the lack of tracking stability and the extensive modification of the whole runway.
As well as the systems already implemented, there are different publications which concern themselves with approaches to solutions for landing aircraft that are designed without an undercarriage for the purpose of reducing mass.
In a publication from 1968, the inventor José Domínguez Rego describes a so-called “Aircraft Landing System” (U.S. Pat. No. 3,380,690), with which the aircraft without an undercarriage lands on a runway equipped with rollers and is transferred to a rail-guided slide at the end of the runway. The axis of rotation of the rollers is arranged at right angles to the runway. To enable aircraft to land on the underside of the fuselage, this would have to be considerably strengthened which would lead to a significant increase in mass. This puts the mass reduction due to omitting the undercarriage system into perspective. Furthermore, the whole runway would have to be fitted with rollers, each of which would have to be designed to be individually damped and braked and would therefore have a high level of system complexity. H.-J. Müller and G. Plankermann offer a further proposed solution in the 2002 publication “Vorrichtung in Form einer bodengebundenen Fahrwerksanordnung zum Starten and Landen von Flugzeugen” (Ground-bound landing gear arrangement for aircraft take-off and landing) (DE 4102271). Here, the use of a conventional runway is entirely dispensed with and a carriage on a magnetic track is used instead. However, this requires the landing maneuver to be accurately positioned. A translatory degree of freedom at right angles to the landing direction to take into account a lateral offset of the aircraft shortly before touching down is completely absent. The lateral offset can come about due to disturbances such as gusts of wind for example, and cannot be ruled out even with the use of automatic landing systems. Furthermore, it is not possible for the apparatus to be jointly used also by conventional aircraft with undercarriage, and the raised course of the magnetic track constitutes a high risk potential.
An “Anordnung mit einer Einrichtung zur Landung von Flugzeugen” (Arrangement having a device for landing aircraft) (DE 19950674) was conceived in 2003 by M. Günther for the emergency landing of aircraft with defective undercarriage and also for routine landings of aircraft without undercarriage, in which a landing platform accelerates along the runway until it is synchronized with the approaching aircraft. The device is laterally guided by rails and is fitted with a catch net and wheels fixed underneath the landing platform.
Because of its large size, the mass of this system will presumably be high and the aircraft will have to be lifted and transported from the landing platform after landing. Furthermore, here too, the underside of the aircraft's fuselage would have to be strengthened to achieve a damage-free landing. It is questionable whether economic operation can be made possible under these boundary conditions for the use of aircraft, particularly in the civil commercial aircraft sector.
In general, it can be said that the solutions presented and similar solutions described in other publications (for example U.S. Pat. No. 3,567,159, U.S. Pat. No. 3,128,066, U.S. Pat. No. 2,246,716, U.S. Pat. No. 6,394,391 B1, DE 3034014) are not suitable for regular flight operations including the landing of aircraft, in particular commercial aircraft, usually not for operational reasons, in particular due to the sometimes considerably complicated ground operations, or because of the necessary extensive modifications to the aircraft, for example to the underside of the fuselage, and the associated higher structural mass.